Concerns of another potential massive viral outbreak continue to increase, following news that nearly 200 people are currently said to be under medical observation in Russia’s Serbia region amid the death of a lab worker, suspected to have been exposed to the pneumonic plague.

According to the Moscow Times, Alexei Tsydenov, head of the neighbouring republic of Buryatiahat confirmed that the worker, identified as 28-year woman, had died from an unspecified form of plague. Russia’s consumer welfare service also reported on Sunday that the researcher at an anti-plague institute in Irkutsk had died of “pneumonia of unknown etiology,” or origin, as NBC

It, however, said that the “sanitary-epidemiological situation” in the Irkutsk region and the cities of Irkutsk and Shelekhov was “stable.”

The incident had prompted health officials to place nearly 200 people who had been in contact with the researcher under precautionary medical observation, Russian media reports. It’s further understood that the inpatient facility where the researcher was treated had been closed for quarantine out of an abundance of caution on Friday.

It’s reported that the incident occurred after the scientist accidentally broke a test tube containing live bacteria while collecting samples for testing. “She was hospitalised Tuesday with symptoms of severe pneumonia in Shelekhov, a town near the regional capital of Irkutsk. Her condition worsened over the following days, as she was placed on a ventilator before eventually passing on Thursday, as per Moscow Times.